The anatomical variant of high soleus muscle may predispose to tendinopathy: a preliminary MR study

Insertional Achilles tendinopathy: A novel link to shorter free tendons

BACKGROUND

Achilles tendinopathy is a common overuse injury among athletes, classified into mid-portion and insertional types. While existing literature primarily emphasizes mid-portion tendinopathy as the more prevalent form, emerging evidence highlights the significance of insertional tendinopathy. Variations in clinical presentation warrant further investigation, particularly regarding anatomical differences that could inform treatment strategies and rehabilitation protocols.

PURPOSE

This study aimed to assess the prevalence of Achilles tendon pathologies and explore anatomical differences in the length of the free tendon between insertional and mid-portion tendinopathy.

STUDY DESIGN

This study represents a cross-sectional analysis conducted as part of a larger longitudinal study on the mechanical properties of patients with Achilles tendinopathy.

METHODS

A total of 103 patients (38.8 % males, 61.2 % females, age: 53 ± 12.8 years, body Mass Index (BMI): 30 ± 7.4 kg/m2, 60 % sedentary while 40 % active) diagnosed with Achilles tendon pathologies from across the Maltese islands were recruited for ultrasound assessments to measure tendon length and evaluate associated anatomical characteristics. Participants were categorised based on the type of tendinopathy.

RESULTS

A higher prevalence of insertional tendinopathy (67.9 %) was identified compared to mid-portion tendinopathy (20.3 %). Notably, participants with insertional tendinopathy presented with short tendons (3.8 ± 1.4 cm, p = <0.001) compared to those with longer free tendon length in mid-portion tendinopathy (5.9 ± 1.3 cm, p = <0.001). This anatomical distinction, along with the lower attachment of the soleus muscle, may contribute to differing biomechanical properties, influencing the risk of specific tendon pathologies.

CONCLUSIONS

This study is the first to report a higher prevalence of insertional tendinopathy and to highlight the link between short free tendon length and insertional tendinopathy. This emphasizes the importance of monitoring short free tendons, as they are likely pivotal in the development of insertional tendinopathy.

Prognostic value of ultrasound tissue characterisation for a recurrence of mid-portion Achilles tendinopathy in military service members: a prospective cohort study

INTRODUCTION

Tendon structure in mid-portion Achilles tendinopathy (mid-AT) appears poorly associated with symptoms. Yet, degenerative tendon changes on imaging have been associated with an increased risk of mid-AT. We aimed to investigate the prognostic value of ultrasound tissue characterisation (UTC) for a mid-AT recurrence in service members reporting to be recovered following standard care.

METHODS

Mid-portion aligned fibrillar structure was quantified post-treatment in 37 participants. Recurrences were determined after 1 year of follow-up, based on self-perceived recurrence (yes/no) combined with a decrease in post-treatment Victorian Institute of Sports Assessment-Achilles score of at least the minimal important change of 7 points. Receiver operating characteristic curve analyses were used to determine a threshold for dichotomisation of outcomes for aligned fibrillar structure (normal representation/under-representation). Using multivariable logistic regression, the association between a mid-AT recurrence (yes/no) and the dichotomised aligned fibrillar structure was determined.

RESULTS

Eight participants (22%) experienced a recurrence. The threshold for aligned fibrillar structure was set at 73.2% (95% CI: 69.4% to 77.8%) according to Youden's index. Values below this threshold were significantly associated with a mid-AT recurrence (odds ratio (OR) 9.7, 95% CI: 1.007 to 93.185). The OR for a mid-AT recurrence was 1.1 (95% CI: 1.002 to 1.150) for each additional month of symptom duration. The explained variance of our multivariable logistic regression model was 0.423; symptom duration appeared to be a better predictor than aligned fibrillar structure.

CONCLUSIONS

This study identified mid-portion aligned fibrillar structure and symptom duration as potential prognostic factors for a mid-AT recurrence in military service members. The threshold for aligned fibrillar structure of 73.2% can guide preventative interventions (eg, training load adjustments or additional tendon load programmes) aiming to improve tendon structure to minimise the future recurrence risk.

TRIAL REGISTRATION NUMBER

https://www.toetsingonline.nl/to/ccmo_search.nsf/Searchform?OpenForm, file number ToetsingOnline NL69527.028.19.

Does free tendon length influence the injury risk of the Achilles tendon? A finite element study

Purpose

The Achilles tendon is a common injury site, but anatomical risk factors for injury are relatively unexplored in the literature. This study aimed to evaluate whether changes in free tendon length would influence the results of a simulated rupture of the Achilles tendon.

Methods

Using a previously validated 3D finite element model of the free and aponeurotic Achilles tendon as a basis, two additional finite element models with 25% decreased and increased free tendon lengths were created. The finite element models were sequentially loaded from 2500 to 3500N in 100N increments, and the total volume of elements exhibiting a maximal principal strain above 10% was recorded. An Achilles tendon rupture was considered to have occurred when a continuous group of elements with a volume of at least 3 mm3 exhibited a maximum principal strain above 10%. Models were compared regarding the smallest load that met the rupture criterion and plots of the percentage of elements exhibiting maximum principal strains above 10% across the loading range. Sensitivity analyses assessed the influence of subtendon division variations and subtendon sliding restriction on the results.

Results

Rupture loads and plots of the percentage of elements with maximum principal strains above 10% were similar between models, regardless of the free tendon length. No models met the rupture criterion when simulations were run without subtendon sliding. Rupture loads in the subtendon division variation models were correlated with the subtendon cross-sectional areas.

Conclusions

The simulated rupture results of the Achilles tendon were sensitive to variations in subtendon cross-sectional areas but not in free tendon length.

Level of Evidence

Level V.

The Distal Free Achilles Tendon Is Longer in People with Tendinopathy than in Controls: A Retrospective Case-Control Study

Objectives

The free Achilles tendon is defined as the region of tendon distal to the soleus which is "unbuttressed," i.e., unsupported by muscular tissue. We reasoned that a relative lack of distal buttressing could place the tendon at a greater risk for developing Achilles tendinopathy. Therefore, our primary goal was to compare the free Achilles tendon length between those with midportion or insertional Achilles tendinopathy and healthy controls.

Design

This is a retrospective case-control study. Setting. Hospital in Vancouver, Canada. Participants. 66 cases with Achilles tendinopathy (25 insertional, 41 midportion) consecutively drawn from a hospital database within a 5-year period and matched to 66 controls (without tendinopathy) based on sex, age, and weight. Main outcome measures. Odds ratio of the risk of developing Achilles tendinopathy given the length of free tendon, defined anatomically on MRI, after adjustment for confounders.

Results

MRI-defined free Achilles tendon length is a statistically significant predictor of having midportion Achilles tendinopathy (odds ratio = 0.53, 95% confidence interval 1.13 to 2.07). Midportion Achilles tendinopathy cases had significantly longer free tendons (Mdn = 51.2 mm, IQR = 26.9 mm) compared to controls (Mdn = 40.8 mm, IQR = 20.0 mm), p = 0.007. However, there was no significant difference between the free Achilles tendon lengths in insertional AT cases (Mdn = 47.9 mm, IQR = 15.1 mm) and controls (Mdn = 39.2 mm, IQR = 17.9 mm), p = 0.158. Free Achilles tendon length was also correlated with the tendon thickness among those with Achilles tendinopathy, rτ = 0.25, and p = 0.003.

Conclusions

The MRI-defined length of the free Achilles tendon is positively associated with the risk of midportion Achilles tendinopathy. A relative lack of distal muscular buttressing of the Achilles tendon may therefore influence the development of tendinopathy.

An Identical Twin Study on Human Achilles Tendon Adaptation: Regular Recreational Exercise at Comparatively Low Intensities Can Increase Tendon Stiffness

Achilles tendon adaptation is a key aspect of exercise performance and injury risk prevention. However, much debate exists about the adaptation of the Achilles tendon in response to exercise activities. Most published research is currently limited to elite athletes and selected exercise activities. Also, existing studies on tendon adaptation do not control for genetic variation. Our explorative cross-sectional study investigated the effects of regular recreational exercise activities on Achilles tendon mechanical properties in 40 identical twin pairs. Using a handheld oscillation device to determine Achilles tendon mechanical properties, we found that the Achilles tendon appears to adapt to regular recreational exercise at comparatively low intensities by increasing its stiffness. Active twins showed a 28% greater Achilles tendon stiffness than their inactive twin (p < 0.05). Further, our research extends existing ideas on sport-specific adaptation by showing that tendon stiffness seemed to respond more to exercise activities that included an aerial phase such as running and jumping. Interestingly, the comparison of twin pairs revealed a high variation of Achilles tendon stiffness (305.4–889.8 N/m), and tendon adaptation was only revealed when we controlled for genetic variance. Those results offer new insights into the impact of genetic variation on individual Achilles tendon stiffness, which should be addressed more closely in future studies.